The algorithm does not support direct positioning. However, by ordering the nodes using a comparator it might be possible to put each element to its space. If not, than you have to implement your own changes - that should not be too hard.

it seems I wasn't clear about my intentions with the comparator. I was asking to try to use the GraphViewer#setComparator method, as it will order the nodes before they are added to the algorithm (at least if I am not mistaken).

Of course, a layout algorithm may also offer a comparator support, but in that case it is their responsibility to handle the data. The GridLayoutAlgorithm does not do this, but relies on the external ordering created by the GraphViewer before.